Dynamic contact stress and rolling resistance model for total knee replacements

Problems associated with premature failure of total knee replacements (TKR's) include: wear, creep and oxidation of ultra high molecular weight polyethylene (UHMWPe) and adverse tissue reactions to polyethylene wear debris. These problems are associated in part with the mechanical behaviour of UHMWPe under the loading conditions experienced in total joint replacements. In TKR's, contact stress analyses have been performed to assess the state of stress on the UHMWPe tibial component. However, previous contact stress models have employed simplified material properties and have not accounted for joint kinematics.

In this thesis, viscoelastic testing of UHMWPe was performed for the development of a three kernel function nonlinear viscoelastic constitutive stress-strain relationship. A rolling resistance model was developed which was based on viscoelastic properties of the UHMWPe component. This model was used to predict the variations in contact stress and rolling friction with rolling speed for total knee replacements.

The results indicated that the contact stress increased and rolling friction decreased with increasing rolling speed. The effects of geometry, applied load and tibial plateau thickness were consistent with previous models. The study suggests that the predicted contact stresses may vary as much as 200% of their static value at large rolling speeds.